At present, with global large-scale construction of 3G network, operators increasingly focus on reducing the construction costs and the maintenance costs. Power amplifier as one of the most expensive devices in the communication system is more and more required to have a higher efficiency, such that the Digital Pre-Distortion (DPD) technology has developed quickly.
In the DPD technology, the DPD processing of signals is performed mainly by pre-distortion coefficients. The pre-distortion coefficients are substantially stored in a pre-distortion coefficient LookUp Table (LUT). In the existing DPD technology, the research on updating LUT is mainly directed to single frequency band signals and a mathematical model of the DPD processing of signals is as follows:
                                          z            ⁡                          (              n              )                                =                                    ∑                              m                =                0                            M                        ⁢                                          x                ⁡                                  (                                      n                    -                    m                                    )                                            ⁢                                                ∑                                      q                    =                    1                                    Q                                ⁢                                                      w                                          m                      ,                      q                                                        ⁢                                                                                                          x                        ⁡                                                  (                                                      n                            -                            m                                                    )                                                                                                                                  (                                              q                        -                        1                                            )                                                                                                                                        =                                    ∑                              m                =                0                            M                        ⁢                                          x                ⁡                                  (                                      n                    -                    m                                    )                                            ·                                                LUT                  m                                ⁡                                  (                                                                                x                      ⁡                                              (                                                  n                          -                          m                                                )                                                                                                  )                                                                                                  =                                    ∑                              m                =                0                            M                        ⁢                                          x                ⁡                                  (                                      n                    -                    m                                    )                                            ·                                                LUT                  m                                ⁡                                  (                                      Q                    ⁡                                          (                                              r                                                  n                          ,                          m                                                                    )                                                        )                                                                                                      LUT          m                ⁡                  (                                                x              ⁡                              (                                  n                  -                  m                                )                                                          )                    =                        ∑                      q            =            1                    Q                ⁢                              w                          m              ,              q                                ⁢                                                                  x                ⁡                                  (                                      n                    -                    m                                    )                                                                                  (                              q                -                1                            )                                            ,                  ⁢          m      =              1        ⁢                                  ⁢        …        ⁢                                  ⁢        M              ,          n      =              1        ⁢                                  ⁢        …        ⁢                                  ⁢        N            
Wherein, rn,m=|x(n−m)| is an amplitude of an input signal, Q(•) is a quantization factor, an input address of LUT depends on a quantized amplitude Q(rn,m) of the input signal, wm,q is a pre-distortion coefficient calculated by DPD adaptive filter, and after calculating the Wm,q, a pre-distortion signal may be acquired by a pre-distortion module.
However, presently there is no suitable method for updating LUT of multi-frequency baud signal. If above processing of single frequency band is used for the signals of each frequency, then the calculation complexity will be high and calculated pre-distortion coefficients will be unstable.